The field of the invention is sodium bicarbonate production and the present invention is particularly concerned with the preparation of sodium bicarbonate and hydrogen chloride by reacting an aqueous sodium chloride solution with carbon dioxide in the presence of an amine and an organic solvent.
The state of the art of sodium bicarbonate production may be ascertained by reference to Israeli Pat. No. 33,552, U.S. Pat. No. 3,443,889 and the Kirk-Othmer "Encyclopedia of Chemical Technology", Second Edition, Vol. 1 (1963) page 734 and Vol. 18 (1969) page 467, the disclosures of which are incorporated herein.
Assignee's U.S. Pat. No. 4,115,530 is incorporated herein to amplify one of the process steps used in the present invention.
A major part of the world production of sodium carbonate is by calcining sodium bicarbonate which is obtained in the Solvey process as an intermediate product from the equation: EQU NaCl+CO.sub.2 +H.sub.2 O+NH.sub.3 .fwdarw.NaHCO.sub.3 +NH.sub.4 Cl
Ammonium chloride is obtained in addition. The ammonia as a rule is recovered from the ammonium chloride by being treated with burnt lime. Large amounts of calcium chloride are also obtained, which together with the unconverted sodium chloride are fed as waste liquor to the sewer system. The drawback of the Solvay process essentially is therefore that all of the chlorine of the reacted sodium chloride is lost in the form of worthless calcium chloride, and that furthermore the unconverted sodium chloride also is lost.
Similar to the case for the Solvay process, the chlorine of the starting material also is lost as disclosed in the method of U.S. Pat. No. 3,443,889 whereby for instance alkali carbonates are prepared from alkali chlorides and carboxylic acid in the presence of a strongly basic amine dissolved in an organic solvent. From the aminohydrochloride that is formed, only the amine is recovered by treating the organic phase with an alkalinically active reagent for the purpose of feeding it back into the process.
Israeli Pat. No. 33 552 discloses the preparation of sodium bicarbonate and hydrogen chloride in a variation of the Solvay process by first treating a heterogeneous mixture of an amine dissolved in a polar organic solvent and a sodium chloride solution with carbon dioxide in a gaseous phase at pressures up to 9 atmospheres. The sodium bicarbonate precipitates from the aqueous phase, the aminohydrochloride produced remains dissolved in the organic phase and is removed. Thereupon, the amine is regenerated from its hydrochloride by treatment with aqueous magnesium hydroxide, the aqueous magnesium chloride obtained then is decomposed at temperatures up to about 500.degree. C. with the formation of magnesium oxide, magnesium oxichloride and hydrogen chloride. Depending on the process conditions, the hydrogen chloride, however, is not exclusively water-free, and therefore it can be used only to a limited extent for industrial purposes. A further drawback of this method is the high temperature required in the production of hydrogen chloride, the increased danger of corrosion related thereto and the use of magnesium salts as additional accessories.